At present there is no accepted and easily used method for measuring human olfactory system performance. As a result, there is no way to determine whether this performance has changed as a result of exposure to environmental chemicals, sickness, medical treatments, age, or other unknown causes. Odor dilutions could be used for such testing, but no satisfactory method for preparing such dilutions is known.
In the past odor dilutions have been prepared either by mixing odorous vapors with odorless gases or by mixing odorous substances in liquid solutions in a solvent which was as close to being odorless as possible. These methods are cumbersome, difficult to accomplish accurately due to surface adsorption effects and slow diffusion times, difficult to verify by quantitive assay since the mixing apparatus or solutions must be transported to the assay facility. In the case of liquid dilutions, the near impossibility of finding a solvent suitable for non-polar substances (which constitute the majority of odorous substances) which is odorless and which has a known molecular composition has been severely limiting. The vapor-phase dilution system is limiting because it does not allow easy use of low concentrations of materials due to the limitations of gas flow metering systems. To achieve low concentrations, liquid dilutions are required with their attendant limitations.